1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by using a perpendicular magnetic recording system and to a method of manufacturing such a magnetic head.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
Like magnetic heads for longitudinal magnetic recording, magnetic heads for perpendicular magnetic recording typically used have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head comprises a magnetic pole layer that produces a magnetic field in the direction orthogonal to the surface of the recording medium. The pole layer incorporates a track width defining portion and a wide portion, for example. The track width defining portion has an end located in a medium facing surface that faces toward the recording medium. The wide portion is coupled to the other end of the track width defining portion and has a width greater than the width of the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in writing characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the writing characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, are reduced. It is therefore required to achieve better writing characteristics as the track width is reduced. Here, the length of the track width defining portion orthogonal to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the above-mentioned medium facing surface. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt called a skew of the magnetic head is created with respect to the tangent of the circular track, in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew is created, problems arise, such as a phenomenon in which data stored on an adjacent track is erased when data is written on a specific track (that is hereinafter called adjacent track erasing) or unwanted writing is performed between adjacent two tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between adjacent two tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
A technique is known for preventing the problems resulting from the skew as described above, as disclosed in the U.S. Patent Application Publication No. US2003/0151850A1 and the U.S. Pat. No. 6,504,675B1, for example. According to this technique, the end face of the track width defining portion located in the medium facing surface is made to have a shape in which the side located backward in the direction of travel of the recording medium (that is, the side located on the air-inflow-end side of the slider) is shorter than the opposite side. Typically, in the medium facing surface of a magnetic head, the end farther from the substrate is located forward in the direction of travel of the recording medium (that is, on the air-outflow-end side of the slider). Therefore, the above-mentioned shape of the end face of the track width defining portion located in the medium facing surface is such a shape that the side closer to the substrate is shorter than the side farther from the substrate.
As a magnetic head for perpendicular magnetic recording, a magnetic head comprising a pole layer and a shield is known, as disclosed in the U.S. Pat. No. 4,656,546, for example. In the medium facing surface of this magnetic head, an end face of the shield is located forward of an end face of the pole layer along the direction of travel of the recording medium with a specific small space therebetween. Such a magnetic head will be hereinafter called a shield-type head. In the shield-type head, the shield prevents a magnetic flux from reaching the recording medium, the flux being generated from the end face of the pole layer and extending in directions except the direction orthogonal to the surface of the recording medium. The shield-type head achieves a further improvement in linear recording density.
The U.S. Pat. No. 5,726,839 discloses a technique for reducing the thickness of a portion of the pole layer (the main pole) near the medium facing surface such that this portion is thinner than the other portion of the pole layer.
The U.S. Patent Application Publication No. US2002/0034043A1 discloses a technique in which a portion of the pole layer (the main pole) near the medium facing surface is made to have a thickness that decreases as the distance from the medium facing surface decreases.
The U.S. Patent Application Publication No. US2002/0080524A1 and the U.S. Patent Application Publication No. US2003/0193744A1 disclose a technique in which a yoke layer thicker than a main pole layer is magnetically coupled to the main pole layer. An end face of the yoke layer closer to the medium facing surface is located at a distance from the medium facing surface.
Here, a combination of the main pole layer and the yoke layer that are disclosed in the U.S. Patent Application Publication No. US2002/0080524A1 and the U.S. Patent Application Publication No. US2003/0193744A1 is called a pole layer for convenience. It is a technique for making a portion of the pole layer near the medium facing surface have a thickness smaller than that of the other portion of the pole layer that is disclosed in each of the U.S. Pat. No. 5,726,839, the U.S. Patent Application Publication No. US2002/0034043A1, the U.S. Patent Application Publication No. US2002/0080524A1 and the U.S. Patent Application Publication No. US2003/0193744A1.
Consideration will now be given to a method of forming a pole layer having a track width defining portion with an end face that is located in the medium facing surface and that has a shape in which the side closer to the substrate is shorter than the side farther from the substrate as described above. It is frame plating that has been often used in prior art for forming such a pole layer. In a method of forming the pole layer by frame plating, an electrode film is first formed on a base of the pole layer. Next, a photoresist layer is formed on the electrode film. The photoresist layer is then patterned to form a frame having a groove whose shape corresponds to the pole layer. Next, plating is performed by feeding a current to the electrode film to form the pole layer in the groove. The frame is then removed. Next, the electrode film except a portion located below the pole layer is removed. Next, an insulating layer made of alumina, for example, is formed to cover the pole layer. Next, the insulating layer and the pole layer are polished by chemical mechanical polishing (hereinafter referred to as CMP), for example. Through the polishing, the top surface of the pole layer is flattened, and the thickness of the pole layer is controlled to be of a desired value.
It is difficult through the foregoing method of forming the pole layer to control the level at which polishing is stopped with precision. If the polishing is stopped at a level other than a desired level, the thickness of the pole layer is made other than a desired thickness, and the track width defined by the length of the above-mentioned side farther from the substrate is thereby made other than a desired value. Therefore, the foregoing method of forming the pole layer has a problem that it is difficult to control the track width with precision.
The U.S. Patent Application Publication No. US2003/0151850A1 discloses a technique in which the end face of the track width defining portion located in the medium facing surface is made to have a shape having a first portion and a second portion. The first portion has a width that continuously increases from an end on the air-inflow-end side to an end on the air-outflow-end side. The second portion is located on the air-outflow-end side of the first portion and has a uniform width that is equal to the width of the end of the first portion on the air-outflow-end side. This technique is capable of reducing variations in track width.
To solve the problems resulting from the skew, it is also effective to reduce the thickness of the track width defining portion taken in the medium facing surface. However, if the thickness of the entire pole layer is reduced, the cross-sectional area of the pole layer orthogonal to the direction in which the magnetic flux flows is reduced. As a result, it is impossible that the pole layer introduces a magnetic flux of great magnitude to the medium facing surface, and the overwrite property is thereby reduced.
In the U.S. Pat. No. 5,726,839, the U.S. Patent Application Publication No. US2002/0034043A1, the U.S. Patent Application Publication No. US2002/0080524A1 and the U.S. Patent Application Publication No. US2003/0193744A1, a portion of the pole layer near the medium facing surface is made to have a thickness smaller than that of the other portion of the pole layer. This results in a reduction in thickness of the track width defining portion taken in the medium facing surface, and thus allows the pole layer to introduce a magnetic flux of great magnitude to the medium facing surface. However, a problem that will now be described occurs in this case. In the above-described technique, it is inevitable that the pole layer has a portion in which the thickness varies. In this portion, it is likely that flux leakage from the pole layer occurs. Consequently, if the portion is close to the medium facing surface, the leakage flux from the portion reaches the medium facing surface and further leaks to the outside from the medium facing surface. As a result, the effective track width is increased and/or the above-mentioned problems resulting from the skew occur.